From BBC News:

But the scale of China’s own entangled history with coal is overwhelming. Right across northern China, coal seams burn in un-stoppable fires.

Some have been burning naturally for thousands of years, but others are being set alight by small-scale mining operations seeking to cash in on soaring coal prices. Together, these perpetual fires are letting off a total amount of carbon dioxide each year equal to all the cars in the USA.

We pay way too little attention to the first word in the phrase “global warming.”